When I ride my recumbent stationary bike in the basement, I can maintain a 135-140 heart rate for about 45 minutes. By the end, my legs feel like they are going to fall off and I am completely soaked in sweat. Outside, my average heart rate is typically 145-150 for short rides (20-30 miles) and 135-140 for long rides (60+ miles).

When I do intervals inside, I often get the pulse up to 165-170, but I can't maintain that for longer than 30-45 seconds. My legs feel fine but I lose my wind. In contrast, I can hold 165-170 outside for a 5+ minute climb.

I have four hypotheses:

(1) Riding outside, the wind evaporates sweat, keeping my body temp down. I can work harder without feeling like I'm working harder.

(2) Riding inside only works my legs. Outside, I bring in core and a bit of arms. Thus, for the same overall effort, my legs are doing less work and can last longer.

(3) Riding outside has breaks for stoplights, coasting down hills, etc. I may think I'm working more steadily than I am.

Recovering now from carpal tunnel surgery last Wednesday so recumbent exerciser is only cycling I'm allowed right now. Have a fan in front blowing on me with towel under to catch sweat. Nothing like riding on the road, 63 soon 2 b 64, 5' 8" @ 135/140lbs, and don't do anything like effort as when on road. Our 32 to 40 mile no stopping AM rides have no hills, SW FL., so constant pedaling with average 23mph plus, max heart 170bpm average 145/150. Just can't match that riding indoors.

The more you ride, the more you'll ride comfortably at a greater effort.

On the recumbent you are getting "recumbent legs" because pedalling on that set-up uses slightly different muscles than on a diamond framed bike.

Other than that, invest in a fan for when you ride inside. There is an element of not using arms, back and shoulders on the recumbent, but personally, I don't think it is as significant as you might think.